The long-term goal of this research is to determine how spinal cord neurons are made with appropriate characteristics to form functional neuronal circuitry. This knowledge is essential for developing effective treatments for spinal cord injuries and neuronal diseases that affect locomotion or sensory perception. In addition, it is likely to provide insights into similar processes that occur in the brain. Most of the functional properties of neurons, that determine the roles that they play in specific neuronal circuits, are thought to b determined by the post-mitotic transcription factors that these cells turn on (express) as they start to differentiate. However, in many cases, it is not known which transcription factors are important for specifying particular functional properties. This is particularly the case for excitatory neurotransmitter fates. Neurotransmitter fates are one of the key defining functional properties of a neuron. Neurons utilizing inappropriate neurotransmitters will not function properly in neuronal circuitry. This proposal focuses on an excitatory class of dorsal spinal cord neurons that express two highly-related transcription factors, Hmx2 and Hmx3. These neurons are involved in sensory perception but very little is known about how they develop their specific functional properties. Preliminary data suggest that Hmx2 and Hmx3 act redundantly to specify the excitatory fates of these dorsal spinal neurons. This project will test this hypothesis and use unbiased systems biology methods to determine the molecular mechanisms through which these two transcription factors act. This project will use zebrafish embryos as a model system as they have several advantages for this research. The embryos develop outside the mother and are optically transparent, enabling neuron morphology and synapse formation to be observed in intact, live embryos. In addition, it is faster and cheaper to test the functions of specific genes in zebrafish embryos than in mammals. Evidence to date, suggests that spinal neurons are highly conserved between zebrafish and mammals, in terms of the genes that they express and their functional properties. Therefore the findings from this work should also be applicable to mammals, including humans. The results from this research will significantly increase knowledge about how spinal neurons are specified and form functional neuronal circuits. This should have a huge impact on the fields of developmental neurobiology and neural stem cell biology. These results should also lead the way towards new treatments for CNS injury and disease. For example, molecules identified in this work may be able to instruct stem cells or neural progenitor cells to develop into excitatory neurons, repress GABAergic fates and/or may provide novel drug targets for conditions such as neuropathic pain.